Porosity of a Fast-Setting Mortar with Crystallization Admixture and Effect of a SA-PA Modification

Abstract

Air permeability measurements according to the Hagen–Poiseuille equation, Scanning Electron Microscopy (SEM) and mercury intrusion porosimetry (MIP) tests were conducted on samples of cementitious mortar at different curing times to study the correlation between the increased crystallization and their microstructure. The mortar samples were prepared with a commercial fast-setting premix containing calcium silicates and quartz. The average permeability coefficient (K) was 2.96 × 10−15 m2 after 3 days and decreased to 3.07 × 10−17 m2 after about one month. The continuous C-S-H nucleation in the capillary pores of the cement mortar changes their shape and improves the mortar’s impermeability. The SEM images showed the development of crystals that refine the pore size distribution of the cement paste, with more of the smallest pores, and fewer of the largest, as demonstrated by the MIP measurements. Adding a superabsorbent polyacrylate (SA-PA) in the amount of 0.5% wt of dry powder, without adding any extra water, makes a mortar less fluid but not faster-setting. Twenty-four hours after mixing and casting, it is still plastic and, with time, the pore size distribution differs from that of standard mortar. Over time in air, permeability remains high, but in water it could be low due to swelling of SA-PA residues.

Cement Pastes with Hygroscopic Polymeric Additions for Potential Building Applications

“…Four different mixtures were prepared and tested during the early stage of aging. The samples were prepared by adding water to a pre-mixed powder, whose phases have been detailed in a previous paper [20], and then mixed for about 20 s. Although the technical data sheet of the pre-mixed powder provided by the manufacturer suggests a lower water/binder ratio for the preparation of the pastes, w/b = 0.4 was used to attain manually workable pastes. Superadsorbent poly-acrylate (SA-PA) and/or nylon fibers (Ny) [20,35] were added to dry powder before mixing it with water.…”

“…All the fresh pastes were cast into molds-polypropylene Petri dishes with 9 cm diameter and rubber molds of 1 cm × 1 cm × 0.3 cm-and vibrated for 30 s [20]. They were aged at different times at 20 ± 2 • C and R.H. 50 ± 5%.…”

“…As recalled before, low permeability is linked to an absence of interconnected porosity: the larger the porosity, the greater the interconnectivity. In a previous study [20], a correlation was established between air permeability and the size of pores during the hydration of cement paste and the continuous growth of CSH crystals. Pore size distribution has been associated with water diffusion: the more CSH forms, the more gel pores, the fewer capillary pores, and the greater the strength.…”

“…The present study considered the effect of the addition of SA-PA and polyamide fibers (Ny) on the pore size evolution and the thermo-mechanical behavior of cement pastes, prepared using a cement mix containing a crystallization admixture. The latter was a calcium silicate, which hydrates quickly, forming crystalline seeds as nuclei for CSH crystallization and promoting the development of strength [20][21][22][23]. Aging progressively reduces the volume and size of pores; therefore, the presence of highly hygroscopic fibers or additions could induce a different pore distribution.…”

Reliability analysis of complex structures based on Bayesian inference

“…That is particularly evident in highly creep-sensible structures, like prestressed concrete box girders. 8 Indeed, their predictions are affected by significant uncertainties, 9,10 and consequently, their reliability analysis might result in an unexpected high probability of failure. The model parameters must be accurately estimated to reduce the uncertainty of model predictions and better estimate the probability of failure of a structure.…”